1. Technical Field of the Invention
The present invention relates generally to the field of photonic crystals; and, more particularly, to a three-dimensional photonic crystal waveguide apparatus.
2. Description of Related Art
Photonic crystals are periodic dielectric structures that can prohibit the propagation of light in certain frequency ranges (see J. D. Joannopoulos, R. D. Meade, and J. N. Winn, Photonic Crystals, Princeton University Press, Princeton, N.J., 1995). In particular, photonic crystals have spatially periodic variations in refractive index; and with a sufficiently high refractive index contrast, photonic bandgaps can be opened in the structure""s optical spectrum. The term xe2x80x9cphotonic bandgapxe2x80x9d as used herein and as used in the art is a frequency range within which the propagation of light through the photonic crystal is prevented. In addition, the term xe2x80x9clightxe2x80x9d as used herein is intended to include radiation throughout the electromagnetic spectrum, and is not limited to visible light.
It is known that introducing defects in the periodic structure of a photonic crystal allows the existence of localized electromagnetic states that are trapped at the defect site, and that have resonant frequencies within the bandgap of the surrounding photonic crystal material. By providing a region of defects extending through the photonic crystal, a waveguide structure can be created and used to control and guide light.
A two-dimensional photonic crystal slab waveguide apparatus may comprise a two-dimensional periodic lattice in the form of an array of posts incorporated in a slab body and having upper and lower cladding layers. The posts can, for example, comprise holes in a slab body of dielectric material, or the posts can comprise dielectric rods and the slab body can be air, another gas or a vacuum. In addition, the posts can comprise rods of a dielectric material having a first refractive index and the slab body can comprise a dielectric material having a second refractive index different from the first refractive index. One example of a two-dimensional photonic crystal slab waveguide apparatus comprises a photonic crystal having a periodic arrangement of posts in the form of air holes arranged in and extending through a dielectric slab body, and a waveguide comprising a region of defects in the photonic crystal formed by omitting some of the air holes (see M. Loncar, et al., Appl. Phys. Lett., 77, 1937, 2000).
In a two-dimensional photonic crystal slab waveguide apparatus, light propagating in the slab is confined in the direction perpendicular to a major surface of the slab via total internal reflection. Light propagation in other directions is controlled by the properties of the photonic crystal slab. Two-dimensional photonic crystal slab waveguide apparatus are able to guide light in a plane of the apparatus (i.e., in a plane parallel to a major surface of the photonic crystal slab; but are not able to guide light in paths which extend in three dimensions. In other words, planar waveguide devices are known for guiding optical signals in two dimensions. In some applications of optical data manipulation it is desirable to move guide optical signals in three dimensions. Therefore, what is needed is a an apparatus for directing and controlling optical signals in more than two dimensions.
The present invention provides a three-dimensional photonic crystal waveguide apparatus that has a three-dimensional photonic crystal. The three-dimensional photonic crystal comprises a plurality of layers arranged one above another, each of the plurality of layers comprising a plurality of elements that are parallel to and spaced from one another. The plurality of elements in each layer are arranged at an angle greater than zero degrees with respect to the plurality of elements in an adjacent layer. The three-dimensional photonic crystal further has an optical waveguide therein that is capable of transmitting light having a frequency within a bandgap of the three-dimensional photonic crystal, the waveguide comprising a first region of defects in a segment of an element in one of the plurality of layers, the first region of defects having a light input, and a second region of defects in at least a segment of an element in an adjacent layer of the plurality of layers, the second region of defects having two light outputs, the first region of defects and the second region of defects intersecting to provide an optical splitter that extends from the one layer to the adjacent layer.
According to an embodiment of the present invention, the first region of defects is created by omitting a segment of an element in the one layer, and the second region of defects is created by omitting at least a segment of an element in the adjacent layer. By omitting elements and/or segments of elements in a selected plurality of layers, a waveguide can be configured that incorporates an optical splitter and that extends from any one of the plurality of layers to any other of the plurality of layers.
According to a further embodiment of the invention, the light input comprises a light input port in the three-dimensional photonic crystal, the second region of defects is created by omitting an entire element in the adjacent layer and the two light outputs comprise two output ports in the three-dimensional photonic crystal to provide an optical splitter having an input port in the one layer and two output ports in the adjacent layer.
According to further embodiments of the invention, the plurality of elements in each layer comprise a plurality of dielectric rods, and the plurality of rods in one layer are arranged perpendicular to the plurality of rods in adjacent layers; and, in addition, the plurality of rods in every other layer are laterally displaced with respect to one another.
A three-dimensional photonic crystal waveguide apparatus according to embodiments of the present invention provides a fully three-dimensional photonic bandgap. Accordingly, total internal reflection is not needed to confine the light. Instead, the light is confined in the low dielectric region of the photonic crystal (e.g., in air) such that the effects of internal losses and dispersion of the high refractive index medium (i.e., the elements) are not so important.
In general, in a three-dimensional photonic crystal waveguide apparatus of the present invention, a waveguide having one or more splitters and which may additionally include one or more bends can be configured to guide light through the apparatus along substantially any desired path with substantially zero loss. With an apparatus in accordance with the present invention, waveguides can be configured to connect different devices in a tightly integrated and compact optical or optoelectronic integrated circuit.
Yet further advantages, specific details and other embodiments of the present invention will become apparent hereinafter in conjunction with the following detailed description of exemplary embodiments of the invention.